Rapid bacteria-detection platform based on magnetophoretic concentration, dielectrophoretic separation, and impedimetric detection

Carbon dots-based fluorescent probe for detection of foodborne pathogens and its potential with microfluidics

Concern about food safety triggers demand on rapid, accurate and on-site detection of foodborne pathogens. Among various fluorescent probes for detection, carbon dots (CDs) prepared by carbonization of carbon-rich raw materials show extraordinary performance for their excellent and tailorable photoluminescence property, as well as their facilely gained specificity by surface customization and modification. CDs-based fluorescent probes play a crucial role in many pathogenic bacteria sensing systems. In addition, microfluidic technology with characteristics of portability and functional integration is expected to combine with CDs-based fluorescent probes for point-of-care testing (POCT), which can further enhance the detection property of CDs-based fluorescent probes. Here, this paper reviews CDs-based bacterial detection methods and systems, including the structural modulation of fluorescent probes and pathogenic bacteria detection mechanisms, and describes the potential of combining CDs with microfluidic technology, providing reference for the development of novel rapid detection technology for pathogenic bacteria in food.

Dielectrophoretic separation/classification/focusing of microparticles using electrified lab-on-a-disc platforms

BACKGROUND

Separation, classification, and focusing of microparticles are essential issues in microfluidic devices that can be implemented in two categories: using labeling and label-free methods. Label-free methods differentiate microparticles based on their inherent properties, including size, density, shape, electrical conductivity/permittivity, and magnetic susceptibility. Dielectrophoresis is an advantageous label-free technique for this objective. Besides, centrifugal microfluidic devices exploit centrifugal forces to move liquid and particles. The simultaneous combination of dielectrophoretic and centrifugal forces exerted on microparticles still needs to be scrutinized more to predict their trajectories in such devices.

RESULTS

An integrated system utilizing two categories in microfluidics is proposed: dielectrophoretic manipulation of microparticles and centrifugal-driven microfluidics, followed by a numerical analysis. In this regard, we assumed a rectangular microchannel with internal unilateral planar electrodes equipped with three equal-sized outlets placed radially on a centrifugal platform where microparticles flow toward the disc's outer edge. The effect of different coordinate-based parameters, including radial and lateral distances (X and Y offsets)/tilting angles toward the radius direction (α), on the particles' movement was investigated. Additionally, the effect of operational parameters, including applied voltage, the microchannel width, the number of enabled electrodes, the diameter of particles, and the configuration of electrodes, were analyzed, and the distributions of particles toward the outlets were monitored. It was found that enhanced particle focusing becomes possible at lower rotation speeds and higher electric field values. Furthermore, the proposed centrifugal-DEP system's efficiency for classifying red blood cells/platelets and Live/Dead yeast cells systems was evaluated.

SIGNIFICANCE

Our integrated system is introduced as a novel method for focusing and classifying various microparticles with no need for sheath flows, having the ability to conduct particles at desired routes and focusing width. Furthermore, the system effectively separates various bioparticles and offers ease of operation and high-efficiency throughput over conventional dielectrophoretic devices.

Dielectrophoresis: Measurement technologies and auxiliary sensing applications

Dielectrophoresis (DEP), which arises from the interaction between dielectric particles and an aqueous solution in a nonuniform electric field, contributes to the manipulation of nano and microparticles in many fields, including colloid physics, analytical chemistry, molecular biology, clinical medicine, and pharmaceutics. The measurement of the DEP force could provide a more complete solution for verifying current classical DEP theories. This review reports various imaging, fluidic, optical, and mechanical approaches for measuring the DEP forces at different amplitudes and frequencies. The integration of DEP technology into sensors enables fast response, high sensitivity, precise discrimination, and label-free detection of proteins, bacteria, colloidal particles, and cells. Therefore, this review provides an in-depth overview of DEP-based fabrication and measurements. Depending on the measurement requirements, DEP manipulation can be classified into assistance and integration approaches to improve sensor performance. To this end, an overview is dedicated to developing the concept of trapping-on-sensing, improving its structure and performance, and realizing fully DEP-assisted lab-on-a-chip systems.

The construction of CRISPR/Cas9-mediated FRET 16S rDNA sensor for detection of Mycobacterium tuberculosis

The simple and efficient detection of nucleic acids is important in the diagnosis of tuberculosis (TB) caused by Mycobacterium tuberculosis (M. tuberculosis). However, base mismatch will lead to false positive and false negative nucleic acid test, which seriously interferes with the accuracy of the final results. Herein, we demonstrated a CRISPR/Cas-9-mediated fluorescent strategy utilizing fluorescence resonance energy transfer (FRET) for the detection of bacteria. High-variable region of M. tuberculosis 16S rDNA fragment was used as the target, and CRISPR/Cas9 was used as the recognition element. The binding of the P1 probe of upconversion nanoparticles (UCNPs) @SiO₂-P1 and the P2 probe of Fe₃O₄@Au-P2 caused the fluorescence quenching of UCNPs. In the presence of the target, the P2 probe hybridized with the target to form double-stranded DNA (dsDNA), which was recognized and cleaved by CRISPR/Cas9, resulting in the breaking of the P1-P2 duplex linkage. UCNPs moved away from Fe₃O₄@Au under a magnetic field, and the fluorescence signal was restored; bacteria were detected under the excitation of a 980 nm laser source. Using the CRISPR/Cas-9-mediated system, the sensor could distinguish single-base mismatches in 10 bases from the protospacer adjacent motif (PAM) region. The limit of detection (LOD) was 20 CFU mL^-1 and the detection time was 2 h. It developed a new way of accurate nucleic acid detection for disease diagnosis.

An efficient DNAzyme-based DNA scaffold for label-free and sensitive bacterial pathogen detection

Even though it is very important, it is still rather difficult to detect minuscule levels of the bacterial pathogen in clinical practice, such as samples from dental implants. We construct here an efficient scaffold for label-free and sensitive Staphylococcus aureus (S. aureus) detection. The precise recognition of target bacteria by the detection scaffold leads to the self-assembly of Chain i and DNAzyme based cleavage of Chain iii. In detail, active DNAzyme conformation is formed based on the hybridization of Chain iii and Chain ii, and a nicking site is generated in Chain iii, making it possible to form a self-primer in Chain i. With the assistance of DNA polymerase, a single-strand DNA chain is added to the 3' terminal of Chain i, in which process the bacteria is released for the complex to bind with a next detection scaffold, forming a signal recycle. Following DNAzyme-based cleavage, the liberated sequences unroll MB and release G-rich sequences that can specifically bind with the fluorescent dye Thioflavin T (ThT), initiating ThT's fluorescence signal production. The approach demonstrates a wide detection range of 10² CFU/mL and 10⁶ CFU/mL with a low limit of detection of 45 CFU/mL based on the developed detection scaffold, offering good prospects in the diagnosis of bacterial illnesses.

Nucleic Acid Quantification by Multi-Frequency Impedance Cytometry and Machine Learning

Determining nucleic acid concentrations in a sample is an important step prior to proceeding with downstream analysis in molecular diagnostics. Given the need for testing DNA amounts and its purity in many samples, including in samples with very small input DNA, there is utility of novel machine learning approaches for accurate and high-throughput DNA quantification. Here, we demonstrated the ability of a neural network to predict DNA amounts coupled to paramagnetic beads. To this end, a custom-made microfluidic chip is applied to detect DNA molecules bound to beads by measuring the impedance peak response (IPR) at multiple frequencies. We leveraged electrical measurements including the frequency and imaginary and real parts of the peak intensity within a microfluidic channel as the input of deep learning models to predict DNA concentration. Specifically, 10 different deep learning architectures are examined. The results of the proposed regression model indicate that an R_Squared of 97% with a slope of 0.68 is achievable. Consequently, machine learning models can be a suitable, fast, and accurate method to measure nucleic acid concentration in a sample. The results presented in this study demonstrate the ability of the proposed neural network to use the information embedded in raw impedance data to predict the amount of DNA concentration.

Culture-Free Quantification of Bacteria Using Digital Fluorescence Imaging in a Tunable Magnetic Capturing Cartridge for Onsite Food Testing

Accurate, onsite detection of pathogenic bacteria from food matrices is required to rapidly respond to pathogen outbreaks. However, accurately detecting whole-cell bacteria in large sample volumes without an enrichment step remains a challenge. Therefore, bacterial samples must be concentrated, identified, and quantified. We developed a tunable magnetic capturing cartridge (TMCC) and combined it with a portable digital fluorescence reader for quick, onsite, quantitative detection of Staphylococcus aureus. The TMCC platform integrates an absorption pad impregnated with water-soluble polyvinyl alcohol (PVA) with an injection-molded polycarbonate (PC) plate that has a hard magnet on its back and an acrylonitrile-butadiene-styrene case. An S. aureus-specific antibody conjugated with magnetic nanoparticles was used to concentrate bacteria from a large-volume sample and capture bacteria within the TMCC. The retention time for capturing bacteria on the TMCC was adjusted by controlling the concentration and volume of the PVA solution. Concentrated bacterial samples bound to target-specific aptamer probes conjugated with quantum dots were loaded into the TMCC for a controlled time, followed by attachment of the bacteria to the PC plate and removal of unbound aptamer probes with wash buffer. The captured bacteria were quantified using a digital fluorescence reader equipped with an embedded program that automatically counts fluorescently tagged bacteria. The bacterial count made using the TMCC was comparable to a standard plate count (R² = 0.9898), with assay sensitivity and specificity of 94.3 and 100%, respectively.